But we're not just damaging our waistlines when our New Year's resolutions fail, said University of California, Berkeley professor, Stefano DellaVigna. When our words don't match our actions, our finances suffer too. (See 5 money resolutions you should make in 2012.)

In his study, "Paying Not To Go To The Gym," DellaVigna found that consumers overpay for gym visits they don't even use. For example, members who sign a contract with a monthly fee over $70 visit the gym 4.3 times on average, paying roughly $17 each visit. But paying per actual visit would be much, much cheaper, he argues; we could get a ten-visit pass which would save us $7 per visit—a savings of $600 per year.